1. Field of the Invention
The invention relates generally to the field of amplification circuits, more particularly, to automatic biasing of amplifiers.
2. Discussion of the Related Art
In a power amplifier, the direct current (DC), or quiescent current biasing point is a critical design parameter. The quiescent current has significant effects on the characteristics and performance, e.g., linearity, signal distortion, power efficiency, etc., of the amplifier. The optimal DC biasing point of a transistor in an amplifier depends on the application of the amplifier and the characteristics of the transistor, which are affected by environmental surroundings such as temperature variations, process variations, and the like.
An example of a power amplifier is the Doherty Amplifier. The Doherty topology has been used widely in sophisticated and high power application. Traditionally, a Doherty amplifier includes a plurality of peaking amplifiers in which each peaking amplifier requires a different bias level. However, the quiescent conditions of these peaking amplifiers are not easily measurable. Further, amplifier devices are known to have varying characteristics that make it difficult to preset all stages to a predetermined value.
Current methods for biasing these peaking amplifiers employ an off-chip bias that is factory set for each peaking amplifier. Similarly, for configurations such as radio-frequency integrated circuits (RFIC) in a Doherty amplifier configuration, two integrated circuits are needed to bias both the carrier amplifier devices and the peaking amplifier devices. In this configuration, at least one of the integrated circuits is an off-chip, factory bias set. However, for amplifier architectures with multiple output stages, this method becomes inefficient and expensive.
The referenced shortcomings are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning biasing for amplifier architecture; however, those mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been altogether satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.